Screw rotor and screw rotor compressor

ABSTRACT

A new rotor for a positive displacement compressor is provided which includes a non-rotating rotor shaft, a rotatable rotor body having end surfaces and surrounding the rotor shaft, and a mechanism for rotating the rotor body around the shaft. The rotor may be either a male rotor or a female rotor, and a positive displacement compressor is also provided which includes the new male rotor, the new female rotor, and an internal drive mechanism. Such positive displacement compressor includes radial induction bearings, and the internal drive mechanism replaces an external drive mechanism.

BACKGROUND OF THE INVENTION

The present invention relates to a rotor and a positive displacementcompressor, and more particularly to a compressor which includes tworotors.

Positive displacement compressors including helical screw compressors aswell as roots compressors are well known in the art. A helicalcompressor employs one male rotor axially aligned with and incombination with one female rotor. Usually the male rotor is the driverotor driving the female rotor. In a compressor, one male rotor iscommonly combined with one female rotor. Such a compressor is usuallyreferred to as a twin helical screw rotor compressor.

An example of a known twin helical screw rotor compressor or screwcompressor is shown in FIGS. 1 and 2 and is described briefly below.

A compressor 100 includes two mutually engaging screw rotors, of which afirst rotor 101 is a male rotor and a second rotor 102 is a femalerotor. The rotors 101, 102 are rotatably mounted in a working chamberthat is delimited by a first end wall 103, a second end wall 104 and abarrel wall 105 that extends between the end walls 103, 104. As can beseen from FIG. 2, the barrel wall 105 has a form that correspondsgenerally to the form of two mutually intersecting cylinders. Thecompressor has an inlet port 108 at the first end wall 103 and an outletport 109 at the second end wall 104.

The male rotor 101 has a rotor body 22 that includes a plurality oflobes 106 and intermediate grooves 111 which extend in a helical linealong the rotor 22. Similarly, the female rotor 102 has a rotor body 23that includes a plurality of lobes 107 and intermediate grooves 112 thatextend in a helical line along the rotor 23. The major part of each lobe107 on the male rotor 101 is located outwardly of the circle of contactwith the female rotor 102, whereas the major part of each lobe 107 onthe female rotor 102 is located inwardly of said circle of contact. Thefemale rotor 102 will normally have more lobes than the male rotor 101.A typical combination is one in which the male rotor 101 has four lobesand the female rotor 102 six lobes, as shown in FIG. 2.

The gas to be compressed, normally air, is delivered to the workingspace of the compressor through an inlet port 108 and is then compressedin V-shaped working chambers defined between the rotors and the chamberwalls. Each chamber moves to the right in FIG. 1, as the rotors 101, 102rotate. The volume of a working chamber decreases continuously duringthe latter part of its cycle, after communication with the inlet port108 has been cut off. The gas is therewith compressed and leaves thecompressor through an outlet port 109. The ratio of outlet pressure toinlet pressure is determined by the built-in volumetric relationshipbetween the volume of a working chamber immediately after itscommunication with the inlet port 108 has been cut-off and its volumewhen it commences communication with the outlet port 109.

The male rotor 101 in FIG. 1 has a shaft 21 around which the rotor body22 is disposed. The male rotor body 22 has a first end surface 4 whichlies in close proximity to the first end wall 103, and a second endsurface 3 which lies in close proximity to the second end wall 104. Thelobes 106 of the male rotor body 22 have crowns 5, shown linearly inFIG. 1. The female rotor 102 in FIG. 1 has a shaft 26 around which therotor body 23 is disposed. The female rotor body 23 includes a first endsurface 27 which lies in close proximity to the first end wall 103, anda second end surface 28 which lies in close proximity to the second endwall 104. The lobes 107 of the female rotor body 23 have crowns 15,shown linearly in FIG. 1.

Such a compressor is coupled to an electrical motor or combustion enginein order to rotate the male rotor 101 and is for example used to enhancethe performance of an engine in a vehicle such as an automobile or toenhance the performance of a fuel cell due a higher inlet pressure ofair or oxygen. As a consequence thereof, the engine or fuel cell can beproduced having a lower volume and mass. Also, there is a need forreducing the volume and weight of such a compressor for superchargingthe engine or fuel cell.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a small compressor.

According to the present invention, a new rotor for a positivedisplacement compressor is provided which includes a non-rotating rotorshaft; a rotatable rotor body having end surfaces and surrounding therotor shaft; and means for rotating the rotor body around thenon-rotating rotor shaft.

In a preferred arrangement, the means for rotating the rotor body aroundthe non-rotating rotor shaft comprises rotor magnets on the rotor body,wherein the magnets are arranged in a circle centered on an axis of therotor body and facing the shaft; and an electrical stator provided onthe shaft in registration with the rotor magnets. When the stator iselectrically energized, the rotor body is caused to rotate about thenon-rotating rotor shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a Prior Art helical rotaryscrew compressor;

FIG. 2 is a sectional view taken on line II-II in FIG. 1;

FIG. 3 is an end view showing two cooperating rotors of the presentinvention;

FIG. 4 is a sectional view of the rotors shown in FIG. 3 taken alongline IV-IV;

FIG. 5 is a sectional view corresponding to the view in FIG. 4 includinga compressor housing; and

FIG. 6 is a sectional view of a radial induction bearing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIGS. 3 and 4 two cooperating rotors for a screw rotor compressoraccording to the invention are illustrated. The left rotor 1 is a malerotor and the right rotor 21 is a female rotor.

The male rotor 1 comprises a rotor body 3 having the shape of acylindrical shell. The outer surface of the rotor body 3 has helicallyextending lobes 6 separated by intermediate grooves 7. As is apparentfrom FIG. 3, the male rotor body 3 has six lobes 6 and the same numberof intermediate grooves 7. The inner surface 10 of the cylindrical shellof the male rotor body 3 is cylindrical. Further, the male rotor body 3has parallel planar end surfaces 4 and 5. Inside of the male rotor body3 a male rotor shaft 2 is arranged. The two end parts 2A and 2B of theshaft 2 extend beyond the end surfaces 4, 5, respectively, of the malerotor body 3.

Two bearings 8, 9 are disposed in a spaced relationship between theshaft 2 and the inner surface 10 of the male rotor body 3. Between thebearings 8, 9 on the inner surface 10 of the male rotor body 3,permanent magnets 11 in the form of rods or bars are placed in parallelsuch that they form a cylindrical shell ring. The magnets 11 are securedto the rotor body 3. The magnets 11 may be arranged in an insert to beplaced inside the rotor body 3 and fixed (i.e., bonded) to the innersurface 10 of the rotor body 3 or may be bonded separately to thissurface 10 as is known in the art.

The male rotor shaft 2 is provided with an axially extending blind bore13 opening in one of the planar ends thereof. Further, a bore 13A in thecylindrical surface of the shaft 2 is connected to (in communicationwith) the axial bore 13.

Electrical windings 12 are wound on the shaft 2 of the rotor 1 betweenthe bearings 8, 9 in registration with the cylindrical shell of magnets11. These windings 12 function as stator leads. End parts 14 of thewindings 12 are passed through the bore 13A from the cylindrical surfaceof the shaft 2 and through the axial bore 13 to the outside of the shaft2 and are connected to an electrical power source 80. The stator leads13 when energized will cooperate with the ring shaped shell of permanentmagnets 11 in the same way as in an electrical motor. In this case,contrary to a conventional electrical motor, the outer part will rotatewhile the central part acts as a stator.

Similarly, as also shown in FIG. 4, the right rotor 21 is a female screwrotor. The female rotor 21 comprises a female rotor body 23 having theshape of a cylindrical shell. The outer surface of the female rotor body23 has helically extending lobes 26 separated by intermediate grooves27. As is apparent from FIG. 3, the female rotor body 23 has eight lobes26 and the same number of intermediate grooves 27. The inner surface 30of the cylindrical shell of the female rotor body 23 is cylindrical.Further, the female rotor body 23 has parallel planar end surfaces 24and 25. Inside of the female rotor body 23 a female rotor shaft 22 isarranged. The two end parts 22A and 22B of the female rotor shaft 22extend beyond the end surfaces 24, 25, respectively, of the female rotorbody 23.

Two bearings 28, 29 are disposed in a spaced relationship between thefemale rotor shaft 22 and the inner surface 30 of the female rotor body23. Between the bearings 28, 29 on the inner surface 30 of the femalerotor body 23 permanent magnets 31 in the form of rods or bars areplaced in parallel such that they form a cylindrical shell ring. Themagnets 31 are secured to the female rotor body 23. The magnets 31 maybe arranged in an insert to be placed inside the female rotor body 23and be fixed (i.e., bonded) to the inner surface 30 of the female rotorbody 23 or may be bonded separately to this surface 30 as is known inthe art.

The female rotor shaft 22 is provided with an axially extending blindbore 33 opening in one of the planar ends thereof. Further, a bore 33Ain the cylindrical surface of the shaft 22 connects to (communicateswith) the axial bore 33.

Electrical windings 32 are wound on the shaft 22 of the female rotor 21between the bearings 28, 29 in registration with the cylindrical shellof magnets 31. The windings 32 function as stator leads. End parts 34 ofthe windings 32 are passed through the bore 33A from the cylindricalsurface of the female rotor shaft 22 and through the axial bore 33 tothe outside of the female rotor shaft 22 and are connected to anelectrical power source 80. The stator leads 33 when energized willcooperate with the ring shaped shell of permanent magnets 31 in the sameway as in an electrical motor. In this case, contrary to a conventionalelectrical motor, the outer part will rotate while the central part actsas a stator.

FIG. 5 shows a sectional view of a compressor which includes the tworotors 1 and 21 of FIG. 4. The compressor housing 40 comprises twoparallel end walls 41 and 42 and a barrel wall 43 between the end walls41, 42. The inside of the barrel wall 43 has the shape of twointersecting cylinders corresponding to the diameters of the two rotors1 and 21. The end parts of the rotor shaft 2, 22 are protruding into theend walls 41, 42 of the compressor housing 40. The configuration of thecompressor housing corresponds to that shown in FIGS. 1 and 2 having aninlet port 44 and an outlet port 45.

FIG. 6 is an enlarged sectional view (not to scale) of a part of a rotorshaft, and shows a radial induction bearing 60 between a shaft 61 and arotor body 70 shown as a cylindrical shell. The shaft 61 is part of thebearing by serving as an inner stator-mounting rod. Two ring shapedaxial magnets 62, 63 are fixed around the mounting rod 61 in a spacedrelationship. The magnets 62, 63 have opposing magnetic directions(polarities). In the space between the magnets a spacer ring 64 isarranged with an iron washer 65 provided around the outside of thespacer ring 64. Also, second and third spacer rings 66, 67 bearingagainst the magnets 62, 63, respectively, are provided. Similarly,outside the spacer rings 66, 67 end plates 68, 69, respectively, arearranged. Such radial induction bearings are known in the art.

Reverting to FIG. 5, the operation of the compressor will now bedescribed. In order to start the rotation of the compressor rotors, thewindings 12, 32 have to be energized. Upon energizing the windings, therotor bodies 3, 23 will start to rotate. In this case both rotors areenergized and separately driven by electrical power. Since the malerotor 1 has 6 lobes and the female rotor 21 has 8 lobes, the rotationalspeeds of these rotors must differ. If the male rotor 1 has a rotationalspeed of N rpm the rotational speed of the female rotor 21 is 0.75N rpm.Generally, if the compressor male rotor has X lobes and the compressorfemale rotor has Y lobes, the rotational speed of the female rotor is(X/Y)*N rpm, where N is the rotational speed of the male rotor.

As seen from the foregoing, according to the present invention, a rotorfor a positive displacement compressor comprises a non-rotating shaftaround which a rotatable rotor body is mounted. The rotatable rotor bodyhas a central bore in which the shaft is inserted. The rotor body has ashape which essentially corresponds to an elongated shell having planarparallel end walls. An outer surface of the rotor body comprises lobesand intermediate grooves helically extending between the end walls.There are typically at least 2 but less than 10 lobes and intermediategrooves. The lobes and grooves extend helically from the outer surfaceof the rotor body. The helical twist is preferably in a range of 5-90°for a roots compressor and 150-330° for a helical screw compressor. Endparts of the rotor shaft extend beyond the rotor body and serve astrunnions. Two bearings are arranged in a space between the rotor shaftand the rotor body in a spaced relationship. The bearings allow therotor body to be rotated relative to the shaft.

Further, on an inner part of the rotor body facing the shaft, magnetsare arranged in a circle around the shaft. Metal wires are wound on theshaft as electrical windings which are arranged such that, when fed withelectrical power, the windings cooperate with the magnets in the rotorbody. This cooperation results in rotation of the rotor body around therotor shaft.

The positive displacement compressor according to the invention thuscomprises a housing including a first and a second end wall, a barrelwall having an inner shape substantially corresponding to twointersecting cylinders between the end walls, an inlet port and anoutlet port for fluid. Two cooperating rotors are mounted in parallel inthe two intersecting cylinders. One of the rotors is a male rotor andthe other one is a female rotor. The two end portions of thenon-rotating shafts of the respective rotors are mounted in the endwalls of the rotor housing.

Each of the rotors comprises a rotor body which has a central bore andis arranged rotatably around the non-rotating shaft, and bearingsmounted on the shaft. The bearings are arranged in a spaced relationshipnear each end of the respective rotor body. Each rotor body is providedwith magnets, preferably permanent magnets, arranged in a circle andfacing the shaft. On the periphery of the shaft there are windings forcooperation with the magnets on the rotor body. Both the windings andthe magnets are arranged between the bearings. The windings have leadswhich are connectable to a power source. When the windings areenergized, the respective rotors are caused to rotate, like a motor.

Each rotor body is provided with lobes and intermediate grooves on theouter surface. The lobes and grooves are preferably arranged as a helix.The male rotor body has usually two or more lobes. The number of lobesof the female rotor body is usually but not necessarily greater than thenumber of lobes of the male rotor body. Such a difference in the numberof lobes requires that the two rotors rotate with different revolutionunits of time.

Additional advantages and modifications will occur to those readilyskilled in the art. For example, although according to the presentinvention each of the rotors 1, 21 is driven by its own source ofenergy, in known compressors a motor drives one rotor while the otherrotor is driven indirectly by the driven rotor or by means ofsynchronizing gears. Additionally, the bearings in the presentcompressor may be conventional bearings, such as roller bearings, orradial induction bearings. Preferably, at least one of the bearings 8, 9and 28, 29, respectively, is a radial induction bearing. Variousadditional modifications may be made without departing from the spiritor scope of the general inventive concept as defined by the appendedclaims and their equivalents.

1. A rotor for a positive displacement compressor comprising: anon-rotating rotor shaft; a rotatable rotor body having end surfaces andsurrounding the rotor shaft; and means for rotating the rotor bodyaround the shaft.
 2. The rotor according to claim 1, wherein the meansfor rotating the rotor body around the shaft comprises: rotor magnets onthe rotor body, wherein the magnets are arranged in a circle centered onan axis of the rotor body and facing the shaft; and electrical statorleads provided on the shaft in registration with the rotor magnets. 3.The rotor according to claim 2, further comprising an electrical powersource and leads connecting the power source to the stator leads.
 4. Therotor according to claim 1, further comprising magnetic inductionbearings between the shaft and the rotor body.
 5. The rotor according toclaim 2, wherein the rotor magnets are arranged between the end surfacesof the rotor body.
 6. The rotor according to claim 1, wherein an outersurface of the rotor body comprises lobes and intermediate grooves. 7.The rotor according to claim 6, wherein the lobes and grooves extendhelically along the rotor body.
 8. A positive displacement compressorcomprising: (i) a housing comprising: a first end wall and a second endwall, a barrel wall having an inner shape substantially corresponding totwo intersecting cylinders between the end walls, an inlet port forfluid, and an outlet port for fluid; (ii) a male rotor mounted in thehousing and comprising: a non-rotatable male rotor shaft protruding intothe end walls, and a rotatable male rotor body surrounding the rotorshaft and extending between the end walls, wherein the male rotor bodycomprises first lobes and first intermediate grooves on an outer surfaceof the male rotor body; (iii) a female rotor cooperating with the malerotor and mounted in the housing parallel to the male rotor, the femalerotor comprising: a non-rotatable female rotor shaft protruding into theend walls, and a rotatable female rotor body surrounding the rotor shaftand extending between the end walls, wherein the female rotor bodycomprises second lobes and second intermediate grooves on an outersurface of the female rotor body; (iv) means for rotating the male rotorbody around the male shaft; (v) means for rotating the female rotor bodyaround the female rotor shaft; and (vi) bearings provided between themale rotor shaft and the male rotor body and between the female rotorshaft and the female rotor body.
 9. The compressor according to claim 8,wherein the means for rotating the male rotor body around the male rotorshaft comprises: rotor magnets in the male rotor body, wherein themagnets are arranged in a circle centered on an axis of the rotor bodyand facing the shaft; and electrical stator leads provided on the shaftin registration with the rotor magnets, wherein the electrical statorleads are connectable to a power source; wherein the means for rotatingthe female rotor body around the female rotor shaft comprises: rotormagnets in the female rotor body, wherein the magnets are arranged in acircle centered on the axis of the rotor body and facing the shaft; andelectrical stator leads provided on the shaft in registration with therotor magnets, wherein the electrical stator leads are connectable to apower source.
 10. The compressor according to claim 8, wherein thebearings are roller bearings.
 11. The compressor according to claim 9,wherein the bearings are roller bearings.
 12. The compressor accordingto claim 8, wherein the bearings are ball bearings.
 13. The compressoraccording to claim 9, wherein the bearings are ball bearings.
 14. Thecompressor according to claim 8, wherein at least one bearing is aradial induction bearing.
 15. The compressor according to claim 9,wherein at least one bearing is a radial induction bearing.
 16. Thecompressor according to claim 8, wherein the lobes and grooves extendhelically along the rotor bodies.
 17. The compressor according to claim9, wherein the lobes and grooves extend helically along the rotorbodies.
 18. The compressor according to claim 16, wherein the bearingsare roller bearings.
 19. The compressor according to claim 17, whereinthe bearings are roller bearings.
 20. The compressor according to claim16, wherein the bearings are ball bearings.
 21. The compressor accordingto claim 17, wherein the bearings are ball bearings.
 22. The compressoraccording to claim 16, wherein at least one bearing is a radialinduction bearing.
 23. The compressor according to claim 17, wherein atleast one bearing is a radial induction bearing.